Conventionally, the assembly of a small-sized precision product, such as an electronic component, requires precision assembling work, since the product uses very small components. In such precision assembling work, for highly accurate assembly, an assembly target object (an intermediate product to which a component(s) is to be attached) and an assembly component (usually, a plurality of assembly components) which are placed on an assembly-target-object-and-assembly-component carrier pallet are led into an assembly section (an assembling station) by use of NC equipment and optical sensors; are transferred to a predetermined positioning apparatus; and are then assembled accurately (Patent Document 1).
In order to cut down an equipment installation space and the cost of equipment, an improved assembling system was proposed (Patent Document 2). In this system, an assembly target object and assembly components required for assembly are placed on a carrier pallet. When the carrier pallet comes to each of assembling stations, a transfer apparatus unloads, from the carrier pallet, an assembly target object placed at a predetermined position on the carrier pallet and positions the assembly target object at a predetermined position at the assembling station. Next, the transfer apparatus unloads, from the carrier pallet, an assembly component placed at a predetermined position on the carrier pallet and attaches the assembly component to a predetermined attachment position on the assembly target object, which has been positioned at the predetermined position at the assembling station. Upon completion of attaching all of the assembly components to the assembly target object in the aforementioned manner, the assembly target object (product) is returned back to the predetermined position on the carrier pallet and is sent to the next step.
Another assembling system (Patent Document 3) is configured as follows. At a component supply station, an assembly target object and a plurality of assembly components of different kinds required for assembly are placed on a carrier pallet. At an assembling station, a robot attaches the assembly components to the assembly target object. When a product model is changed, component holding jigs, which are removably held on the carrier pallet, are replaced as appropriate according to assembly components of a new product model. Then, assembling work is carried out in a similar manner.    Patent Document 1: Japanese Patent Application Laid-Open (kokai) No. S63-295128    Patent Document 2: Japanese Patent Application Laid-Open (kokai) No. H05-084676    Patent Document 3: Japanese Patent Application Laid-Open (kokai) No. 2002-326127
However, according to the assembling systems described in Patent Documents 1 and 2, an assembly target object and assembly components are led to assembling stations so as to undergo assembling work. This requires a wide space for installation of equipment and apparatus required for assembling work. Also, much time is consumed in transferring the assembly target object and assembly components to the assembling stations, resulting in inefficiency.
Further, according to the assembling system described in Patent Document 3, a robot carries out attachment of a plurality of assembly components of different kinds at a single assembling station. This renders complex the structure of a holder head of the robot for holding an assembly component, control of the robot, and the configuration of peripheral accessory apparatus. Additionally, when a transfer motion in plane is involved, a moving mechanism for movement in plane is required. This involves the accumulation of mechanical errors of the moving mechanism, resulting in impairment in accuracy in attaching assembly components to an assembly target object. Thus, an error in attachment is apt to arise.